1. Field of Invention
The present invention relates to a catalyst for polymerization and copolymerization of ethylene. More particularly, the invention relates to a solid titanium complex catalyst for polymerization and copolymerization of ethylene. Embodiments of the catalyst system include a solid titanium complex catalyst supported on a carrier containing magnesium. The catalyst displays high catalytic activity whereby polymers of high bulk density and narrow molecular weight distribution may be produced.
2. Description of Related Art
The polymerization of ethylene is usually carried out in the liquid phase in the presence of a solvent such as isopentane or hexane, or in the gas phase. The important factors affecting the polymerization in these processes are: polymerization activity and hydrogen reactivity of the catalyst, bulk density of the resulting polymers, the amount of monomers soluble in the solution, particle size distribution, and the existence of fine particles in the resulting polymers. The molecular weight distribution of the resulting polymers is one of the major factors in determining the physical properties of the resulting resin. The physical properties of resin may be improved by the use of a catalyst that can produce a polymer or copolymer of ethylene having a narrow molecular weight distribution.
Recently, many methods using titanium-based catalysts containing magnesium have been reported for polymerization and copolymerization of olefins. These catalysts may provide high catalytic activity, produce polymers of high bulk density, and are known to be suitable for liquid phase and gas phase polymerization.
For example, when using a magnesium solution to obtain a catalyst which may produce olefin polymers of high bulk density, the magnesium solution is prepared by reacting magnesium compounds with an electron donor. Electron donors include alcohols, amines, cyclic ethers, or organic carboxylic acids. The magnesium solution is prepared in the presence of a hydrocarbon solvent. A magnesium supported catalyst may be prepared by reacting the magnesium solution with halogen compounds such as titanium tetrachloride. Methods using an alcohol to prepare a magnesium solution are disclosed in U.S. Pat. Nos. 3,642,746, 4,336,360, 4,330,649, and 5,106,807. Also, U.S. Pat. Nos. 4,477,639 and 4,518,706 disclose a method which uses tetrahydrofuran or a cyclic ester as the solvent for dissolving the magnesium compound. Although these catalysts may produce polymers of high bulk density, the catalysts need to be improved regarding catalytic activity of the catalyst and molecular weight distribution of the resulting polymers.
In addition, U.S. Pat. Nos. 4,847,227, 4,816,433, 4,829,037, 4,970,186, and 5,130,284 have reported the preparation of olefin polymerization catalysts which have good polymerization activity and can enhance the bulk density of resulting polymers. Increased polymerization activity was achieved by reacting electron donors such as magnesium, alkoxide, dialkylphthalate or phthaloyl chloride with a titanium chloride compound. U.S. Pat. No. 5,459,116 has reported a method for preparing a titanium solid catalyst by contacting a magnesium solution containing an ester having at least one hydroxyl group as an electron donor with a titanium compound. By this method, it is possible to obtain a catalyst which has high polymerization activity and affords high bulk density in resulting polymers, but there is much to be improved regarding molecular weight distribution of the resulting polymers.
Therefore, there is a demand for catalysts for polymerization and copolymerization of ethylene which may be prepared by a simple process, have high polymerization activity and controlled particle size, and which can produce polymers having narrow molecular weight distribution.